It is known in the art to use a scrubber unit to remove impurities from air. It is recognized that the scrubber unit will contain a packing or filter material through which the polluted air will move and which is wet by a scrub or wash fluid. The type of filter and wash fluid used depends on the type of impurities which are to be separated and removed from the air. Generally, for effective removal of impurities from air, however, specific filter structures and/or specialty chemicals are required. Such filters normally require regeneration and use of specialty chemicals can result in high cost.
For example, U.S. Pat. No. 4,460,552 discloses a process for separating and removing impurities from air. The impurity-containing air is fed into a scrubber unit and passed through a filter material having an absorbent medium sprayed thereon. The filter pack is described as being one or more packs of stratified filter mats having a specified structure for removing the impurities from the air. The absorbent medium which is sprayed over the filter mats is stated to depend on the particular impurity to be removed, i.e., when an alkaline-reacting impurity is to be absorbed, an acidic absorbent is utilized and when an acid-reacting impurity is to be absorbed, an alkaline absorbent medium is utilized. If the impurity is soluble in water, acidic or alkaline-reacting aqueous solutions can be utilized in the filter process. In columns 6-7 of the patent, scrubber operations using the filter mats of the patent are compared with the operation of conventional packed columns, with each scrubber using the same absorbent medium. Improved results, as shown by the increased recovery over the conventional scrubbers, are attributed to the use of the specified filter mat structure.
U.S. Pat. No. 4,172,880 states that it is recognized in the art to remove pollutants from the air prior to exhaust of the air from an industrial production area through the use of a scrubbing tower. A scrubbing tower suitable for use includes inert material as packing which is wet by a downward spray of fluid. The patent states that in the metal casing industry where the air contains contaminants such as triethylamine, dimethylethylamine, ammonia, or the like, in trace quantities that an acid solution can be used as a scrubbing liquid.
U.S. Pat. No. 2,560,635 discloses a scrubbing apparatus wherein a gas passes upward through a scrubbing or baffle means, such as touching balls. A wash fluid flows downward over the baffle means from a spray outlet positioned above the baffle means as the gas flows upward through the baffle means. The wash fluid utilized can be water alone, an aqueous solution, or any other suitable fluid. The only specific gas referred to for removal is S.sub.2 which when contacted with wash water is changed to H.sub.2 SO.sub.3.
Accordingly, the art does not disclose the use of a pH-adjusted water as a wash fluid in a packed scrubber unit utilizing only an inert material as packing to remove essentially all of the organic impurities from air present in foam processing plants where the organics to be removed include toluene diisocyanate (TDI). More particularly, the art does not disclose the removal of one or more organic pollutants, which are neither acid nor basic, from air as water-soluble solids using a pH-adjusted wash water with only inert packing. Even more specifically, the removal of toluene diisocyanate from air utilizing acidic water is not taught in the art.